Papers
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Geotechnical characterization of a novel material obtained by injecting a closed cell expansive polyurethane resin into a sand mass
This paper reports the findings of experimental studies on a novel application of a closed cell expansive polyurethane resin injection into a sand mass, regarding some common engineering properties.Previous papers on injecting expansive polyurethane resins into sand masses as mitigation measures ofdifferent hazards, e.g., liquefaction, settlements and seismic displacements, deal with the open cell sub-class ofpolyurethane resins. Seeking to make up for the shortcomings of open cell methods, the paper addresses aprototype application of a closed cell polyurethane resin for ground improvement/control on sands.A new system for the preparation of the sand-resin mixture (SRM), which mimics the field application conditions, is introduced. It allows to inject the polyurethane resin into saturated sand with a prescribed massdensity.The results of an extensive laboratory testing program are presented and discussed regarding some relevantengineering properties, e.g., Young
Year: 2023
Number Pages:
14p..
Author(s): Gomes, R.C.; Bilé Serra, J.; Caldeira, L.; Miranda, L.
: Transportation Geotechnics
Editor: Elsevier
Volume:
42 (2023) 101051.
Keywords: Ground improvement; Injection; Closed cell expansive polyurethane resin; Sand mass; Laboratory testing
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Effective stress in unsaturated soils: Lessons from capillarity in regular sphere arrangements
In this paper, capillary stresses and water retention of regular arrangements of rough spherical particlesare analysed to shed light on the effective stress in unsaturated soils. These arrangements can be usedto model soils with uniformly graded round particles such as sand as they are simpler to analyse due totheir symmetries. Capillary stress determines the effective stress in unsaturated sphere arrangementsand is highly dependent on the morphology of the soil voids. In general, it is shown that capillary stress and water retention dependence on suction and degree of saturation in regular arrangements of spheres is more complex than usually assumed with relevant implications for unsaturated soil mechanics and its effective stress. It is also shown that: (i) sphere roughness explains the observed disappearance of capillary stresses in sand with drying; (ii) the capillary stress evolution with suction (or RH) is non monotonic; (iii) it is possible to have significant capillary stresses at zero suction in regular and irregular sphere arrangements, and the Bishop
Year: 2022
Number Pages:
19p.
Author(s): Cardoso, R.; Pereira, C.; Maranha, J.
: Geomechanics for Energy and the Environment
Editor: Geomechanics for Energy and the Environment
Keywords: Spreres' regulsr arragements; Particle-scale behaviour; Water retention; Efective stress; Capilarity forces; unsaturated soils
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Site characterization for the design of thermoactive geostructures
This paper addresses the topic of site characterization for the design of Shallow Geothermal Energy (SGE) systems, namely of thermoactive geostructures, which are geotechnical structures, such as piles, retaining walls and tunnel linings, also used as heat exchangers as part of closed-loop SGE systems. Such solutions, being increasingly adopted for buildings and infrastructures heating and/or cooling, are considered sustainable and cost effective. For the design of the primary circuit of the SGE system, which is embedded within the superficial soil layers, a comprehensive knowledge of the ground condition at the site is mandatory. This includes the evaluation of the energy features and whether the system can provide the required energy needs during the operational period, as well as the verification of the structural and geotechnical safety and functionality requirements. The site characterization for SGE systems involves different stages, from desk studies to detailed characterization, including in-situ trials, laboratory testing of undisturbed soil samples and the study of possible interferences. The specific aspects that will be addressed are: (i) the assessment of the site undisturbed ground temperature and its hydrogeological features; (ii) the thermal and thermomechanical characterization of the different soil layers; (iii) the investigation of the ground-heat exchanger thermal resistance; (iv) the collection of information related to the environmental constraints and to potential interferences among multiple users, which are related to the service life of the structure. The overall aim is to ensure a proper design of the SGE system for guaranteeing its sustainability in the long term.
Year: 2022
Author(s): Vieira, A.
: Soils and Rcks
Editor: ABMS, SPG
Volume:
Special Issue: Thermal Applications in Geotechnical Engineering, January-March, 2022.
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Climate Change Adaptation of Geo-Structures in Europe: Emerging Issues and Future Steps
Climate change is already being felt in Europe, unequivocally affecting the regions
Year: 2021
Number Pages:
24p..
Author(s): Löfroth, H.; Szymkiewicz, F.; Prodan, I.; Pereira, C.; Bra
: Geosciences
Editor: MDPI
Keywords: risk assessment monitoring; nacional strategies; cilmate change impacts; cilmate change effects; climate change signals; geo-tructures; adaptation; climate change
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Dynamic behaviour of Tagus River sand including liquefaction
In the framework of a third Tagus River crossing, through an immersed tunnel, advanced laboratory tests were performed on its highly liquefiable foundation sand. To characterize the cyclic behaviour of the sand and to support the use of advanced constitutive models in the design of the tunnel, key to simulate liquefaction realistically in such a complex project, five cyclic undrained torsional tests were executed. These tests, in which imposed strain increases progressively until and during liquefaction, considering strain amplitude levels with a limited number of cycles, allow a more thorough study of the phase after initial liquefaction than the usual test with constant stress amplitude and the necessary number of cycles to attain liquefaction. Additionally, they provide high quality data, essential to calibrate advanced constitutive models. From their analysis, it is concluded, as expected, that the number of cycles until initial liquefaction increases with relative density and confining pressure. Moreover, while before initial liquefaction maximum excess pore pressure amplitude is due to sand softening and consequent pore pressure build-up, after initial liquefaction it usually happens at the first cycle, being related to an initial higher dilation tendency, before particles loose contact. Finally, the damping ratio increases until a peak value, and then, just before initial liquefaction, generally decreases till the end of the test.
Year: 2020
Number Pages:
24p.
Author(s): Miranda, L.; Caldeira, L.; Bilé Serra, J.
: Bulletin of Earthquake Engineering
Editor: Springer Nature
Keywords: Torsion; Laboratory tests; Immersed tunnels; Sands; Liquefaction; Soil dynamics
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Reviewing the Modeling Aspects and Practices of Shallow Geothermal Energy Systems
Shallow geothermal energy systems (SGES) may take different forms and have recently taken considerable attention due to energy geo-structures (EGS) resulting from the integration of heat exchange elements in geotechnical structures. Still, there is a lack of systematic design guidelines of SGES. Hence, in order to contribute towards that direction, the current study aims at reviewing the available SGES modeling options along with their various aspects and practices. This is done by first presenting the main analytical and numerical models and methods related to the thermal behavior of SGES. Then, the most important supplementary factors affecting such modeling are discussed. These include: (i) the boundary conditions, in the form of temperature variation or heat flow, that majorly affect the predicted thermal behavior of SGES; (ii) the spatial dimensions that may be crucial when relaxing the infinite length assumption for short heat exchangers such as energy piles (EP); (iii) the determination of SGES parameters that may need employing specific techniques to overcome practical difficulties; (iv) a short-term vs. long-term analysis depending on the thermal storage characteristics of GHE of different sizes; (v) the influence of groundwater that can have a moderating effect on fluid temperatures in both heating and cooling modes. Subsequently, thermo-mechanical interactions modeling issues are addressed that may be crucial in EGS that exhibit a dual functioning of heat exchangers and structural elements. Finally, a quite lengthy overview of the main software tools related to thermal and thermo-hydro-mechanical analysis of SGES that may be useful for practical applications is given. A unified software package incorporating all related features of all SGES may be a future aim.
Year: 2020
Author(s): Christodoulides, P.; Vieira, A.; Lenart, S.; Maranha, J. R.; Florides, G.
: Energies
Editor: MDPI
Volume:
Volume 13.
Keywords: software tools; modeling; thermo-hydro-mechanical; thermal analysis; energy geostructures; shallow geothermal energy systems
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Improved subloading thermo-viscoplastic model for soil under strictly isotropic conditions
This paper presents a thermo-viscoplastic subloading soil model with a mobile centre of homothety. The model is formulated to describe the influence of non-isothermal conditions on the stress
Year: 2018
Author(s): Vieira, A.; Pereira, C.; Maranha, J.
: Geomechanics for Energy and the Environment
Editor: Elsevier
Keywords: subloading model; thermal viscoplasticity; soil thermal behaviour
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Numerical modelling of slope
The behaviour of natural and artificial slopes is controlled by their thermo-hydro-mechanical conditions and bysoil
Year: 2017
Author(s): Osinski, P.; Lollino, P.; Helm, P.; Stirling, R.; Askarinejad, A.; Nocilla, A.; Josifovski, J.; Koda, E.; Esch, J.; Rouainia, M.; Springman, S. M.; Pereira, C.; Vardon, P.; Vaunat, J.; Pedone, G.; Cot
: Quarterly Journal of Engineering Geology and Hydrogeology
Editor: Lyell Collection - Geological Society Publications
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Strain-rate change effects in reconstituted London clay using a viscoplastic subloading model
This paper illustrates the capability of a viscoplastic subloading model recently proposedin reproducing strain-rate change effects in soil. The viscoplastic model used is based onthe subloading surface concept making possible the occurrence of viscoplastic strainsinside the yield surface. After a brief description of the basic principles and constitutiverelations behind the model, a numerical simulation of an undrained triaxial compressiontest on a normally consolidated reconstituted London clay with several strain-ratechanges was performed with success. This result was obtained with a general soil modelwhich did not take into account these specific temporary effects in its formulation. Theinfluence of the strain
Year: 2016
Author(s): Vieira, A.; Pereira, C.; Maranha, J.
: European Journal of Environmental and Civil Engineering
Editor: Taylor & Francis
Keywords: strain- accelaration; undershootings; overshootings; subloading visocoplasticity; strain-rate change
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A viscoplastic subloading soil model for rate-dependent cyclic anisotropic structured behaviour
This paper presents a new purely viscoplastic soil model based on the subloading surface concept with a mobile centre of homothety, enabling the occurrence of viscoplastic strains inside the yield surface and avoiding the abrupt change in stiffness of the traditional overstress viscoplastic models. This is required for overconsolidated soils. The model is formulated to reproduce the soil rate-dependent behaviour under cyclic loading (changes in loading direction) and incorporates both initial and induced anisotropy, as well as destructuring. The model shows good qualitative response to some imposed three-dimensional stress paths under quasi-inviscid (elastoplastic) behaviour. Some of the main time-dependent aspects of soil behaviour that the model is capable of reproducing were also illustrated. The capability of the model to adequately reproduce the results from an undrained triaxial test performed on stiff overconsolidated clays from the Lisbon region (Formação de Benfica), with an unloading
Year: 2015
Author(s): Vieira, A.; Pereira, C.; Maranha, J.
: International journal for numerical and analitycal methods in geomechanics
Editor: John Wiley & Sons, Ltd.
DOI:
10.1002/nag.2494
Keywords: struted soil; cyclic loading; anisotropy; subloading surface; overstress viscoplasticity
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Comunicação
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Estudo da condutividade térmica dos solos em Lisboa
O projeto de investigação GeoSustained, financiado pela Fundação Portuguesa para a Ciência e a Tecnologia (FCT, PTDC/ECI-CON/1866/2021), visa estudar soluções sustentáveis utilizando sistemas geotérmicos superficiais para climatização de edifícios e infraestruturas, sob as condições climatéricas e geológicas ocorrentes na cidade de Lisboa. No contexto do projeto, serão instalados furos de monitorização contínua datemperatura no terreno em locais selecionados da cidade. Antes da colocação de séries de termopares dispostos em profundidade, serão recolhidas amostras intactas representativas das principais formações geológicas de Lisboa para ensaios laboratoriais, onde serão obtidas as suas características termofísicas, destacando-se a condutividade térmica. Esta propriedade, será também estimada por via de modelos semi-empíricos, através das frações volumétricas das diferentes fases do solo e, ainda, com base em valores, ou gamas de valores, resultantes de compilações de resultados de ensaios realizados em unidades geológicas semelhantes, disponíveis na bibliografia.Os aspetos mais relevantes deste estudo inicial relativo ao estudo das propriedades térmicas dos solos de Lisboa a diferentes escalas, que virá a fornecer importantes elementos para o futuro planeamento da cidade, são aqui descritos e analisados.
Year: 2023
Author(s): Pereira, C.; Almeida, I. M.; Miguel, I.; Aljundi, K.; Pinto, C.; Vieira, A.
Editor: Sociedade Portuguesa de Geotecnia
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ENSAIOS PARA MEDIÇÃO DE CONDUTIVIDADE TÉRMICA EM AREIAS: ASPETOS DE MODELAÇÃO NUMÉRICA
A avaliação das propriedades térmicas dos solos, em especial da sua condutividade térmica, tem assumido uma importância crescente, sendo essencial para o dimensionamento de sistemas geotérmicos superficiais. Apresentam-se neste trabalho, alguns aspetos de um estudo relativo à medição e modelação de ensaios de condutividade térmica em amostras de solo, conduzidos em regime transitório
Year: 2022
Author(s): Vieira, A.; Pereira, C.; Aljundi, K.; Maranha, J. R.
Editor: Conference proceedings
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Ensaios para medição de condutividade térmica em areias: aspetos de modelação numérica
A avaliação das propriedades térmicas dos solos, em especial da sua condutividade térmica, tem assumido uma importância crescente, sendo essencial para o dimensionamento de sistemas geotérmicos superficiais. Apresentam-se neste trabalho, alguns aspetos de um estudo relativo à medição e modelação de ensaios de condutividade térmica em amostras de solo, conduzidos em regime transitório.
Year: 2022
Author(s): Maranha, J. R.; Aljundi, K.; Pereira, C.; Vieira, A.
Editor: TEST&E 2022
Keywords: modelação numérica; regime transitório; condutividade térmica; ensaios em solos
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A general mathematical framework for modelling soil-water retention behaviour
A new constitutive model to reproduce the soil-water retention behaviour of unsaturated soils is proposed, able to reproduce the main drying and wetting paths, the cyclic retention behaviour and its dependence on the specific volume. The most significant aspect is the inclusion of the evolution, with the specific volume, of the degree of saturation when suction tends to zero in wetting paths considering the presence of entrapped air bubbles. The model is used to reproduce with success the drying/wetting cycles of two Pearl clay samples
Year: 2021
Author(s): Cardoso, R.; Maranha, J.; Pereira, C.
Editor: 3rd Pan-American Conference on Unsaturated Soils
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DEM analysis of some effects due to capillary forces in sands
In this paper, the Discrete Element Method is used to study the e ect of capillary forces, in equilibrium with the ambient relative humidity, on the response of irregular arrangements of equal-sized spheres, simulating a fine uniformly graded quartz sand. The e ect on the isotropic compression was investigated by applying an increase in total stress under constant relative humidity (wet and dry) and drying under di erentconstant total stress values. The e ect of the capillary forces on the shear strength was evidenced by the simulation of the instability of a cylindrical sand column due to drying.
Year: 2020
Author(s): Cardoso, R.; Maranha, J. R.; Pereira, C.
Editor: E-Unsat 2020 (publicação online)
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Laboratory Testing and Numerical Modelling of the Dynamic Behaviour of Tagus River Sand
In the framework of a third Tagus River crossing, through an immersed tunnel, advanced laboratory tests were performed on its highly liquefiable foundation sand, namely cyclic undrained torsional tests. The Manzari-Dafalias model, which allows simulating liquefaction on the Tagus River sand and is, therefore, central in the tunnel design, as well as the numerical work to calibrate the model and identify its most relevant parameters, are presented. Model parameters, their respective reference values and tests performed to determine directly most of the parameters, are introduced. A parameter sensitivity analysis, conducted through numerical simulation of triaxial monotonic drained tests and of cyclic undrained torsional tests, implemented both for the pre-liquefaction and liquefaction phases, is described. Finally, some parameters are determined by fitting the model to the laboratory results.
Year: 2019
Number Pages:
8.
Author(s): Miranda, L.; Caldeira, L.; Bilé Serra, J.
Editor: ISSMGE
Keywords: immersed tunnel; liquefaction; numerical simulation; constitutive model; advanced laboratory tests
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Laboratory Testing and Numerical Modelling of the Dynamic Behaviour of Tagus River Sand
In this paper, an immersed tunnel case-study, corresponding to a third Tagus river crossing, supported on liquefiable alluvial sands, is presented. Laboratory testing, namely monotonic drained triaxial tests and cyclic undrained torsional tests, is described. Moreover, a constitutive model, as well as the numerical work, essential to its calibration and to identify its most relevant parameters, are presented. Model parameters, their respective reference values and tests performed to determine directly most of the parameters, are introduced. A parameter sensitivity analysis, conducted through numerical simulation of triaxial monotonic drained tests, is defined. Furthermore, a parameter sensitivity analysis through numerical simulation of cyclic undrained torsional tests, implemented both for the pre-liquefaction and liquefaction phases, is described. Finally, some parameters are determined by fitting the model to the laboratory results.
Year: 2018
Number Pages:
12.
Author(s): Miranda, L.; Caldeira, L.; Bilé Serra, J.
Editor: LREC
Keywords: immersed tunnel; numerical modelling; advanced laboratory testing; liquefaction; Tagus River sand
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The role of evolutionary algorithms in soil constitutive models
The complex nature of soil behaviour must be modelled with advancedconstitutive models. However, some difficulties can be highlighted that hinder the use and the development of advanced constitutive soil models in geotechnical research andpractice: the objective evaluation of the performance of model variants, the objectivecomparison between different models, the information on the effect of individualparameters (material model constants and initial values of internal variables) on themodel
Year: 2018
Author(s): Maranha, J. R.; Pereira, C.
Editor: 9th European Conference on Numerical Methods in Geotechnical Engineering
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Parameter Sensitivity Analysis of the Manzari-Dafalias Model for Modelling the Cyclic Response of a Sand
In this paper, the numerical work that has been done to calibrate the Manzari-Dafalias model and to identify its more relevant parameters is presented. The model parameters, their respective reference values and the tests that were performed to determine most of the parameters are introduced. A parameter sensitivity analysis through numerical simulation of a triaxial monotonic drained test, using an OpenSees model with a single 1x1x1 m3 SSPbrickUP 3D element, is described and the results analyzed. The sensitivity analysis is conducted for each parameter individually, for several pairs of physically related parameters and of the most relevant ones. It is considered the final influence upon the peak values of the shear strain, shear stress ratio and dilatancy and upon the critical state volumetric strain. Furthermore, a parameter sensitivity analysis through numerical simulation of a cyclic undrained torsional test is implemented, both for the pre-liquefaction and liquefaction phases. In the former, the variation of some response parameters (namely the damping ratio, the shear modulus, the shear stress amplitude, the average shear stress, the shear strain amplitude and the average p) with the model parameters is evaluated for three different cycles.
Year: 2017
Author(s): Miranda, L.; Bilé Serra, J.; Caldeira, L.
Editor: ACHISINA
Keywords: Liquefaction; Torsional test; Triaxial test; Sensitivity analysis; Manzari-Dafalias model; Sand
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Thermo-viscoplastic subloading soil model for isotropic stress and strain conditions.
This paper presents a thermo-viscoplastic subloading soil model with a mobile centre of homothety. The model is formulated to describe the influ-ence of non-isothermal conditions on the stress-strain-time behaviour of soils and is restricted to isotropic stress and strain conditions. Numerical simula-tions of three isotropic drained heating tests at constant isotropic effective stress for different overconsolidation ratios were performed. The model was able to accurately reproduce the experimental results.
Year: 2017
Author(s): Vieira, A.; Pereira, C.; Maranha, J. R.
Editor: International Workshop on Advances in Laboratory Testing and Modelling of Soils and Shales, Villars-sur-Ollon
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Capítulo de Livro
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Influence of ground water level on shallow foundation design. Application of EC7 probabilistic and deterministic methods. Modern Geotechnical Design Codes of Practice
The influence of ground water level on shallow foundation design is presented for the ultimate limit state of the bearing resistance, according to the formulation presented in annex D of EN 1997:2004. Probabilistic and deterministic methods were used and compared. Concerning probabilistic methods, the advanced first-order second-moment method (AFOSM) was applied and the results were validated by Monte Carlo simulations. For the deterministic calculation, the partial factors method recommended by the Eurocode and applied in most practical cases, was implemented. For the assumptions herein made the width B determined by the probabilistic method is always smaller than the one obtained deterministically.
Year: 2013
Author(s): Pereira, C.; Caldeira, L.
: Modern Geotechnical Design Codes of Practice: Implementation, Application and Development
Editor: IOS Press
Keywords: probabilistic methods; partial factor method; bearing resistance; hasofer-lind merthod; shallow foundation
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Tese de Doutoramento
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Formulation of an advanced effective stress based constitutive model for unsaturated soils
The main purpose of the thesis is to show that it is viable the use of a correct effective stress framework to model the behaviour of unsaturated soils, with the development of an adequate effective stress model being an essential factor. One of the main advantages of this methodology is the separation between the solid skeleton mechanical constitutive models, which can be those developed for saturated soils, and the effect of the partial saturation on the behaviour of the soil, being only influenced by the effective stress model. The effective stress framework consists on the solid skeleton mechanical, the soil-water retention and the effective stress models. An isotropic effective stress model is proposed based on the main characteristics of the effective stress evolution in cubic spheres arrangements, incorporating hysteretic behaviour between drying and wetting paths and the dependency of specific volume and temperature, and being a function of the degree of saturation. A soil-water retention model is also proposed incorporating the hysteretic behaviour existent in drying and wetting paths, its dependency of specific volume and the incorporation of unsaturated states with zero suction. A rate-dependent (viscoplastic) and a rate-independent (elastoplastic) mechanical constitutive models, formulated with the subloading concept and the same hardening laws, was presented. The mechanical models can reproduce the cyclic, anisotropic and structured behaviour. Additionally, it is presented their expansion to nonisothermal conditions and the convergence of the response of the viscoplastic model to the elastoplastic model, when dealing with rate-independent soil behaviour (the elastoplastic model being more efficient). A generalised mixed stress-strain control for both viscoplastic and elastoplastic models in non-isothermal conditions is given. The effective stress framework constituted by the proposed mathematical models can reproduce with success diverse and complex unsaturated laboratory tests, reproducing the main aspects of the unsaturated soils behaviour. It is concluded that with an adequate effective stress model, it is not necessary to modify the mechanical constitutive models, previously formulated for saturated soils, introducing dependence of several model parameters on suction, degree of saturation or other similar variables. Also, it is shown that with an adequate evolutionary algorithm, the number of parameters is no longer a relevant issue restraining the use of these complex constitutive models. A newversion of the Differential Evolution method is developed to calibrate constitutive models for the laboratory tests.
Year: 2020
Author(s): Pereira, C.
Keywords: Differential evolution method; Non-isothermal constitutive models; Micromechanical models of spheres; Effective stress model; Unsaturated soils
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Liquefaction mitigation measures: prospective application to immersed tunnel foundations
A state-of-the-art revision of immersed tunnels is done. The selected case-study for this thesis, an immersed tunnel for crossing Tagus River between Algés and Trafaria, is presented. Next, cases of earthquake-induced liquefaction and its associated mechanism are discussed. The most relevant constitutive models for the numerical simulation of the response of soils under cyclic loading are described, including the Manzari-Dafalias model. Subsequently, Tagus River sand is physically characterized and six monotonic drained triaxial tests are analysed, with the goal of characterizing the stress-strain behaviour of the sand and obtain its parameters. Five cyclic undrained torsional tests are also analysed with the goal of characterizing cyclic behaviour of the sand. Then, the calibration framework for the Manzari-Dafalias model is presented, combining results of laboratory tests with numerical sensitivity studies. A parameter sensitivity analysis is carried out to understand the relevance of some chosen model parameters, by using an OpenSees constitutive driver, both through numerical simulation of monotonic drained triaxial tests and of cyclic undrained torsional tests. Some model parameters are calibrated directly from triaxial testing. The remaining parameters are calibrated through numerical simulation and curve fitting of the model to the laboratory results. A new constitutive driver is implemented in MATLAB to clarify some of the Manzari-Dafalias model issues, namely in the liquefaction phase. Finally, multiple liquefaction mitigation measures, and their application in immersed tunnels, are described. Laboratory testing of a mitigation measure, specifically injection of a duromeric expansive polyurethane resin, commercially available, is accomplished. The physical characteristics of both the resin and of the sand-resin mixture are presented. A series of tests, namely high frequency ultrasonic pulse tests, uniaxial compression and tensile tests, and triaxial compression tests, are performed. The modulus of elasticity, the Poissons ratio, the uniaxial compressive and tensile strengths, the triaxial compressive strength and the shear strength parameters, are determined. Two additional injection tests are executed to check densification of the sand between injection columns and its relative density is determined. Finally, the main conclusions are summarized and guidelines for future developments are established.
Year: 2019
Author(s): Miranda, L.
Keywords: Tagus River sand - expansive polyurethane resin mixture; numerical modelling; advanced laboratory testing; liquefaction; immersed tunnels
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Ancoragens pré-esforçadas em obras geotécnicas - Construção, ensaios e análise comportamental.
Os objectivos deste projecto inserem-se no âmbito dos trabalhos desenvolvidos no Núcleo de Fundações, Taludes e Obras de Suporte, do Departamento de Geotecnia do Laboratório Nacional de Engenharia Civil (LNEC/DG/NFTOS), e pretende realizar-se um estudo do comportamento das obras ancoradas, respondendo a solicitações do mercado exterior e por outro lado analisar um tipo de obras que são uma prática constante e cujo comportamento a médio e longo prazo não se encontra devidamente analisado na literatura da especialidade. Esta dissertação objectiva ser um contributo para o dimensionamento, construção e ensaios de ancoragens pré-esforçadas em terreno, isto é, pretende-se com este trabalho elaborar um documento de apoio bibliográfico para a indústria nacional associada à construção de ancoragens. Pretende ainda permitir compatibilizar e estabelecer procedimentos de projecto e construtivos em conformidade com as normas e com a finalidade de garantir a qualidade desejável na construção de ancoragens, para garantir a vida útil prevista das obras de Engenharia. De acordo com o mencionado desenvolvem-se e apresentam-se matérias consideradas importantes para atingir essas finalidades. Analisa-se a bibliografia relativa à documentação normativa e regulamentar, considerada mais relevante, com um levantamento generalizado desses elementos, onde é avaliada a relevância relativa de cada um dos aspectos tratados, comparando-se e confrontando-se os diferentes documentos em assuntos comuns. Abordam-se questões associadas ao dimensionamento e com os factores de segurança de ancoragens. Para tal considera-se a bibliografia relevante e em vigor. Havendo a preocupação em garantir a durabilidade das obras e sendo a integridade física das ancoragens uma preocupação na garantia da sua vida útil aborda-se a problemática da corrosão, dos diversos tipos de corrosão e das classes de protecção das ancoragens contra a corrosão. Indicam-se ainda métodos expeditos para avaliar a carga corrosiva do meio e seu efeito na selecção do tipo de protecção a considerar para as ancoragens. Para optimizar os trabalhos associados às ancoragens, desenvolvidos no LNEC, e o desenvolvimento de novas metodologias relacionadas com obras de suporte com ancoragens definitivas pretende-se preencher algumas lacunas, nomeadamente no que se refere à viabilização da homologação de tecnologias de ancoragens com a participação do LNEC. Estando disponíveis no mercado diversos sistemas de ancoragens e havendo a possibilidade de recorrer a diversas tecnologias apresenta-se algumas referências nessa área e aborda-se diversos aspectos construtivos e tecnológicos. Sendo corrente o compromisso entre a qualidade final da obra, a mão-de-obra e outros factores construtivos, analisa-se a temática da qualidade das ancoragens e das estruturas ancoradas. Apresenta-se uma referência aos diferentes tipos de ensaios de carga, a realizar nas ancoragens, bem como o número e tipo de controlo que a bibliografia recomenda para a sua realização. Indicam-se os critérios de análise e respectivas metodologias. Sendo o factor de fluência, ks, um parâmetro condicionante do comportamento dos solos, a médio e longo prazo, pretende-se calcular o seu valor a partir dos ensaios de carga realizados nas ancoragens. Face aos problemas associados ao cálculo de ks a partir dos ensaios de carga, desenvolveu-se um modelo capaz de simular todos os aspectos de carga e descarga, integrados no ensaio, incluindo os patamares de fluência, e realizam-se análises com a finalidade de esclarecer esses problemas, propondo-se procedimentos para optimizar as estimativas correspondentes. Consideram-se os ensaios de carga primordiais para a caracterização mecânica das ancoragens e para avaliar o comportamento da estrutura de suporte ancorada. Apresenta-se um sistema de ensaios automático (SEA) para o controlo dos ensaios de carga de ancoragens in situ, que se desenvolveu no âmbito deste trabalho. Relativamente a aplicações futuras desse sistema, SEA, apresenta-se a metodologia utilizada pelo LNEC no controlo das blocagens e no cálculo da tracção residual ou efectiva de blocagem.
Year: 2009
Author(s): Carvalho, M.
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Dissertação de Mestrado
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Influência da variabilidade geotécnica na subsidência devida à escavação de túneis urbanos
Na presente tese descreve-se a geometria da subsidência devida à escavação de túneis. Apresentam-se expressões empíricas que se baseiam no volume unitário de subsidência e na distância ao plano de simetria do túnel dos pontos de inflexão da curva teórica de subsidência. Analisa-se, então, as soluções algébricas existentes para a estimativa do campo de deslocamentos, que consideram os efeitos da contracção pura do túnel e da sua ovalização. Descreve-se, ainda, a problemática da modelação numérica bidimensional e tridimensional, fazendo referência aos diversos métodos de simulação do faseamento construtivo. Para poder analisar a influência da variabilidade e correlação espacial das propriedades do terreno nas estimativas de assentamentos causados pela escavação de túneis tem de se recorrer à Teoria dos Campos Aleatórios e à caracterização estatística dos parâmetros geotécnicos. Apresentam-se no capítulo 3 valores das estimativas de medidas estatísticas bem como algumas metodologias de modelação numérica da variabilidade espacial, das quais se destaca a que se baseia na transformada rápida de Fourier espacial. Desenvolvem-se duas ferramentas computacionais para analisar os deslocamentos à superfície causados pela escavação de túneis. A primeira baseia-se no método de Monte Carlo e nas formulações analíticas apresentadas e é aplicada à análise estatística e caracterização de bacias de subsidência em terreno argiloso ligeiramente sobreconsolidado. A segunda baseia-se na geração de campos aleatórios correlacionados espacialmente e permite avaliar a influência da variabilidade espacial dos parâmetros do terreno na dispersão dos assentamentos superficiais. Com base nesta última, compara-se os resultados numéricos com resultados observacionais dum caso de obra.
Year: 2011
Author(s): Miranda, L.
Keywords: variabilidade espacial; campos aleatórios; assentamento superficial; túneis
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Análise distorcional de solos aluvionares lodosos
Casos recentes de rotura desenvolvidos em fundações lodosas, em condições não drenadas, pelo peso de aterros altos (h>9,0 m), tais como os ocorridos durante a construção de aterros na Azambuja e nos terrenos da futura EXPO98 fizeram sobressair a necessidade de desenvolver métodos expeditos, baseados em dados de campo, para estimativas de: i) parâmetros característicos do comportamento de tensões-deformações de solos lodosos; ii) factor de segurança local. De facto, a expansão da cidade de Lisboa e arredores sobre zonas cujo subsolo é constituído por depósitos aluvionares lodosos, de espessuras consideráveis (e>10 m), caracterizados por valores de Cup reduzidos e valores de sensibilidade relativamente altos, tornam o desenvolvimento dos métodos acima referidos uma contribuição importante. Nesse sentido propõe-se: i) Obtenção de parâmetros característicos do comportamento de tensões-deformações de solos lodosos a partir dos resultados obtidos nos ensaios de Molinete efectuados no subsolo lodoso da Azambuja Teixeira Duarte (1994 a 1996). Confirmação desses parâmetros por intermédio de ensaios de laboratório (triaxiais e corte simples) em amostras, não remexidas, recolhidas de furos de sondagem efectuados no local pela Teixeira Duarte para fins de investigação; ii) Simulação analítica desses mesmos ensaios e da construção do aterro, usando o método de elementos finitos (MEF); iii) Obtenção de valores de distorção horizontal, induzidos, em profundidade no subsolo lodoso da Azambuja pelo peso de aterros, a partir dos registos inclinométricos efectuados no local (LNEC, 1994); iv) Estimativas de factores de segurança local com base nos valores obtidos em i) e iii).
Year: 2003
Number Pages:
304.
Author(s): Carvalho, M. R.
Keywords: Ensaio laboratorial; Ensaio in situ; Ensaios de solos; Deformabilidade de solos; Solo aluvionar
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Relatório Científico
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Plano de expansão do Metropolitano de Lisboa. Prolongamento das linhas amarela e verde (Rato
N/A
Year: 2023
Author(s): Pinto Pereira, C.; Miranda, L.; Carreto, J.
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Plano de expansão do Metropolitano de Lisboa. Prolongamento das linhas amarela e verde (Rato
N/A
Year: 2023
Author(s): Miranda, L.; Pinto Pereira, C.
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Thermal conductivity of sand under transient conditions - TPSYS02 Thermal Measurement System
The growing concerns about the climate change and the negative environmental impacts of heating and cooling systems operated by fossil fuels, have led the technical and the scientific communities to find out more environmentally and sustainable energy alternatives, such is the case of shallow geothermal sources. Shallow geothermal systems use the ground as a heat reservoir, transferring thermal energy from the ground to a building, or vice-versa, with the help of a heat pump, to provide warmth in winter and cooling in summer. A proper evaluation of the thermal properties of the soil is essential in their design process and for a sustainable system. Thermal conductivity is the most important parameter for this evaluation. Thermal conductivity can be estimated or measured by several methods, namely by means of empirical correlations, and experimentally, either in situ, by means of the well-known Thermal Response Tests (TRT), or in the laboratory, under steady state or transient conditions. This work presents a series of thermal conductivity measurements on dry sand samples obtained by means of a high accuracy system with reference TPSYS02 Hukseflux equipped with Non-Steady-State Probes (NSSP) (TP02 or TP08). The system was acquired in the aim of an FCT research project. The work includes the completion of a guide to procedures to the use of the thermal measurement system. Details of its calibration as well as results from tests in soil samples are also presented.
Year: 2019
Author(s): Aljundi, K.; Vieira, A.
Keywords: Guide to procedures; Calibration; Shallow geothermal energy systems; Thermal needles; Laboratory tests; Soil thermal conductivity
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Reflexão sobre a qualidade dos dados inclinométricos - Proposta para implementação de um sistema para controlo da qualidade metrológica dos instrumentos de medição angular
N/A
Year: 2011
Number Pages:
133pp.
Author(s): Coimbra, L.
Editor: LNEC
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Cortina de contenção periférica do mosteiro de Santa Clara-a-Velha - Relatório de análise da informação disponível
N/A
Year: 2009
Number Pages:
196pp.
Author(s): Carreto, J.
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Projecto travessia Norte-Sul - Ramal de Alcântara
Este relatório tem como objectivo a apresentação e análise dos resultados obtidos nas campanhas de observação e nas visitas de inspecção realizadas até ao mês de Janeiro de 2007, inclusive. Considera-se, assim, que com a apresentação deste relatório ficam concluídos os planos de trabalhos relativos aos períodos de observação de 2005 e 2006.
Year: 2007
Number Pages:
97p.
Author(s): Sousa, A. G.; Salgado, F. M.
Keywords: Ramal de alcântara; Travessia norte-sul
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Análise distorcional de solos aluvionares lodosos
N/A
Year: 1998
Author(s): Carvalho, M. R.
Keywords: rotura; segurança; distorção; Solos aluvionares
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ICT
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Dimensionamento de ancoragens
Esta publicação objectiva ser um contributo para o dimensionamento de ancoragens pré-esforçadas em terreno. Pretende, também, permitir compatibilizar e estabelecer procedimentos de verificação do dimensionamento de projecto de sistemas ancorados, em conformidade com as normas e com a finalidade de garantir a vida útil prevista das obras de sistemas ancorados. Analisa-se a bibliografia relativa à documentação normativa e regulamentar, mais relevante. Avalia-se a importância relativa de cada um dos aspectos tratados, considerando-se a bibliografia relevante em vigor, comparando-se os diferentes documentos e abordando aspectos associados ao dimensionamento e aos coeficientes de segurança de ancoragens. O conceito associado ao sistema constituído por uma estrutura ancorada visa gerar uma massa de solo internamente estável para um nível de carga de serviço adequado. O dimensionamento das obras de suporte realiza-se, na maioria dos casos, pela análise de condições correspondentes a estados limites últimos, aplicando um determinado valor para o coeficiente de segurança, isto é, para situações correspondentes a equilíbrio limite. No caso de obras de suporte ancoradas, há que considerar também os riscos associados às ancoragens propriamente ditas. Desta forma, na maioria dos casos, impõem-se limites de deslocamentos, do terreno e da estrutura, face às limitações de esforços a que se podem submeter os suportes e as ancoragens nas diversas fases da vida da obra. Por outro lado, no dimensionamento da ancoragem como elemento estrutural, devem considerar-se as diversas exigências de cada uma das partes que a constitui, quer ao nível de desempenho, quer ao nível das acções consideradas.
Year: 2011
Number Pages:
107pp.
Author(s): Carvalho, M. R.; Salgado, F. M.
Editor: LNEC
Keywords: Segurança de estrutura; Estado limite último; Coeficiente de segurança; Estrutura de suporte; Ancoragem em terreno; Ancoragem em betão pré-esforçado
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Outro
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Plano de expansão do Metropolitano de Lisboa. Prolongamento das linhas amarela e verde (Rato
N/A
Year: 2024
Author(s): Carreto, J.; Miranda, L.; Pinto Pereira, C.
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Plano de expansão do Metropolitano de Lisboa. Prolongamento das linhas amarela e verde (Rato
N/A
Year: 2024
Author(s): Pinto Pereira, C.; Miranda, L.
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Plano de expansão do Metropolitano de Lisboa. Prolongamento das linhas amarela e verde (Rato
N/A
Year: 2024
Author(s): Carreto, J.; Miranda, L.
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Plano de expansão do Metropolitano de Lisboa. Prolongamento das linhas amarela e verde (Rato
N/A
Year: 2024
Author(s): Miranda, L.; Pinto Pereira, C.
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Prolongamento da linha amarela. Rato
Apreciação do plano de contingência da Obra Especial 3 no lote 2 na extensão da linha amarela do Metro de Lisboa. Esta obra inclui a transferência de carga do edifício para uma laje de recalçamento fundada em colunas de jet grouting reforçadas com perfis metálicos.
Year: 2024
Author(s): Ramos, R.; Carreto, J.
Keywords: Plano de Contingência; Obra Especial 3; Linha amarela; Metropolitano
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Observação das obras geotécnicas da linha de caminho de ferro da Beira Alta adjacentes à albufeira da Barragem da Aguieira. Observação em 2022. Recomendações para a IP. Memorando.
São explicitadas, neste documento, as alterações ao sistema de observação, devidas às obras de reabilitação da linha ferroviária, bem como as anomalias identificadas nas obras geotécnicas da linha de caminho de ferro da Beira Alta, adjacentes à albufeira da barragem da Aguieira, que se entende extravasarem o âmbito de atuação da EDP, por não ser o Dono de Obra da infraestrutura ferroviária. Estas foram observadas na visita de inspeção visual realizada a 27 de dezembro de 2022, com a participação de representantes da EDP, da IP e do LNEC. São igualmente apresentadas as recomendações para a correção das anomalias identificadas e para a reposição do sistema de observação. Este memorando baseia-se integralmente no relatório:
Year: 2023
Author(s): Miranda, L.
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Análise dos elementos relativos ao colapso do muro de suporte de terras na Avenida Almirante Gago Coutinho que delimita as propriedades nos 73/75, em Lisboa e posterior reconstrução. Recomendações do
N/A
Year: 2022
Author(s): Vieira, A.
Keywords: memorando, muro de suporte
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